Environmental Health Criteria 214

HUMAN EXPOSURE ASSESSMENT
Exposures to contaminants in food may be directly measured by
collecting meals as prepared for consumption by members of the study
population; such samples are often termed duplicate portion samples.
Duplicate portion study designs provide food samples as actually
consumed, rather than samples of unprepared, individual food items
that are typical of surveillance approaches to characterizing dietary
exposures (US NRC, 1993). This distinction is important because the
method by which food is prepared for consumption (e.g., washed, washed
and cooked, or commercially processed) can influence contaminant
residues. In addition, some pollutants can be generated during
cooking, for example, benzo [a]pyrene (Waldman et al., 1991a) and
heterocyclic amines (Skog et al., 1998). Thus, residue levels measured
in duplicate portion samples are likely to more accurately reflect
personal dietary ingestion exposures than raw agricultural commodities
and other foods collected at the producer, processor or distributor
level. Depending on the objectives of the study, water may also be
included as part of the duplicate portion sample.
Duplicate portion study designs use either collection of
individual servings or meals or composite samples. In studies of this
type, participants are often monitored over one or more days, and the
duplicate portion samples are collected daily over the monitoring
period. The former affords a detailed examination of contaminant
levels in specific commodities or foods comprised of several
commodities; however, the analytical chemistry costs associated with
this degree of temporal resolution may be prohibitive. Composite
samples provide an integrated measure of dietary exposure and provide
an efficient means for characterizing total dietary exposures. Both
collection schemes require a high level of effort from study
participants, and the complex food matrices may present analytical
chemistry challenges.
Duplicate portion studies require a high degree of participation
by the study respondents, because they are primarily responsible for
preparation and storage of an additional serving of every food or meal
consumed over the monitoring period. This burden makes it difficult to
collect representative samples of all foods consumed by the
respondent, especially when food is relatively expensive or scarce or
is consumed outside the home. Respondent burden also makes it
difficult to conduct studies of chronic dietary exposures using the
duplicate portion approach. Additional information on assessment of
dietary exposure, including both direct and indirect approaches, may
be found in Chapter 7.4 as well as WHO (1985a, 1995c); EC (1997a).
3.5.1.3 Personal monitoring of dermal absorption exposures
Personal monitoring of dermal exposure is used for those
situations where a pollutant comes in contact with the skin and intake
occurs via absorption through the skin. Dermal patches and skin wipe
samples are used to evaluate exposures for residues adhering to the
surface of the skin (US EPA 1992b; Fenske, 1993; Geno et al., 1996;
Shealy et al., 1997). These methods have typically been used for
industrial hygiene assessments where very high exposures are expected.
Dermal patches and skin wipe samples have been used to characterize
transfer of pesticide residues from soil and grass to skin as well as
spot concentrations of residues on skin (Fenske et al., 1991). Dermal
absorption can also occur during bathing, showering or swimming. In
this case, the contaminant is in the water and exposure occurs when
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